The Democratic Party is moving faster and more aggressively than in previous election years to dig up unflattering details about Republican challengers. In House races from New Jersey to Ohio to California, Democratic operatives are seizing on evidence of GOP candidates' unpaid income taxes, property tax breaks and ties to financial firms that received taxpayer bailout money.

Renacci's campaign said the candidate did not believe he had tax liabilities for a trust fund and eventually paid all that he owed. A spokesman for Harmer said criticizing him for the money he lawfully earned is a "severe twist of the facts." Runyan's campaign said his actions were legal.

Jon Vogel, executive director of the DCCC, said Democrats are merely pointing out that some Republican recruits in competitive House races are "flawed candidates."

He added, "We have made this election a choice. . . . They're trying to run this national message in part about fiscal discipline, but they've recruited a number of candidates not credible to carry that message."

Opposition research has been a part of political campaigns for decades, but the 2010 cycle is different. In many states, Republicans have steered clear of candidates with long political track records -- eschewing state representatives and veteran city council members who have cast thousands of votes ripe for scrutiny -- in favor of political outsiders. The top GOP recruits include several former professional sports stars, as well as doctors and businessmen.

Democratic leaders are trying to frame the November midterm elections not as a national referendum on the party in power but as local choices between two candidates.

"We can win the contrast, but not the referendum," Democratic strategist Steve Murphy said. "What is critical in this election cycle is for Democratic candidates to hold Republican candidates accountable for their views."

Republicans see the Democrats' strategy as a sign of weakness.

"When the issues are cutting against you, it is typical for a party in trouble to resort to other means," said Ken Spain, spokesman for the National Republican Congressional Committee. "With the unemployment rate unacceptably high and President Obama's approval rating falling, they have nothing left to run on other than character assassination."

Democratic officials are advising campaigns to hire trackers to follow their Republican opponents to public events with video cameras, ready to catch any gaffe or misstatement. And the Democratic National Committee last week issued a call to the public to submit any embarrassing audio or video of Republicans, as well as copies of their direct-mail advertisements.

Party officials would not say how many staffers are working on opposition research. Such work used to be farmed out to campaign consultants, but the DCCC brought research operations in-house in 2008 to be more nimble. "It may appear to be more aggressive this cycle because what we're finding on Republicans is so rich," Vogel said.

In Ohio, Democrats are trying to exploit Renacci's business record in his race against Rep. John Boccieri (D). Renacci, who owns a Chevrolet dealership, nursing homes, real estate investments and sports teams, among other interests, has faced a string of lawsuits related to his businesses.

Democratic operatives circulated a report in April that Renacci owed nearly $1.4 million in unpaid state taxes, interest and penalties. Renacci fought the assessment, believing the money he was holding in a trust was free of state tax liabilities. But after losing a dispute over his liability, Renacci paid everything he owed, said his campaign manager, James Slepian.

"This is a story that the DCCC was pushing pretty hard," Slepian said. "It's unfortunate that John Boccieri has chosen to conduct his campaign by slinging mud from behind Nancy Pelosi's desk rather than talking about the issues that really matter."

But Democrats say the strategy paid dividends in the May special election for the Pennsylvania House seat of the late Democrat John P. Murtha. Republican Tim Burns framed the race as a referendum on Obama and House Speaker Nancy Pelosi (D-Calif.), both unpopular in a district that Obama lost to Sen. John McCain (R-Ariz.) in 2008. But Democrat Mark Critz won handily after tailoring his message to local concerns and attacking Burns for saying he would protect tax breaks for companies that ship jobs overseas.

"Some years you ride the wave, and other years you paddle your canoe," Democratic strategist Paul Begala said. "Democrats, they've got to paddle like hell. So what you do when you're paddling is, as the Republicans seek to nationalize, you localize and personalize."